Containers, and more specifically bottles, are widely used in the consumer goods industry for packaging various types of fluid products, such as drinks, foodstuffs, laundry and household cleaning products, shampoo and other personal care products. Thermoplastic materials are mostly used for producing these containers. Typical thermoplastic material used for producing containers and bottles include polyvinylchloride (PVC), polyethylene terephthalate (PET), polypropylene (PP), low or high density polyethylene (LDPE or HDPE) and polystyrene (PS).
Such containers, and more specifically bottles, are required to have certain properties. Indeed, such containers need to have very good mechanical strength to withstand, for example, the rigours of transport, storage and use. These rigours include e.g. stacking of bottles on top of each other (topload), vibrations, shaking and other mechanical stresses, additionally temperature fluctuations during transportation, and usual handling stresses, such as being dropped and squeezed during consumer use. Thus, important mechanical properties include resistance to compression and flexion, and temperature fluctuations. However, these containers must have, at the same time, a weight as low as possible in order to keep material consumption and the resulting environmental footprint, as well as transportation effort, low. In addition, such containers are also required to provide a high level of aesthetic appeal to consumers.
Polypropylene is a polyolefin (or polyalkene) compound and is derived from crude oil. Environmental, economic and sustainability questions are restricting the use of products derived from this limited resource. Therefore, there is a desire to identify more sustainable and effective materials that can be used to replace or partially replace the polyolefin component, whilst meeting the physical requirements discussed above.
The use of fillers to replace some of the thermoplastic material, or even to change the properties of thermoplastic materials, is known in the art. For example, carbon black is known to accelerate the degradation of polypropylene following exposure to UV light. Furthermore, various inorganic fillers have been used in combination with polyethylene—kaolin, mica, diatomite and talc, for example. These fillers tend to be economically affordable and widely available.
Injection moulding, described hereinafter, is a very commonly used process for manufacturing such containers. In conventional injection moulding processes the rate-limiting step of the moulding cycle is the cooling step, which correlates with the thickness of the moulded part. Energy is stored as heat across the gauge of the part and must be transferred into the mould during the cooling cycle. Hence parts with a lower surface area to volume ratio cool more slowly. Cooling time has a significant impact on the speed and hence production capacity of injection moulding equipment, ultimately translating into a greater number of production stations.
There is a need, therefore, for the provision of an improved process for making injection-moulded parts, which maintains the suitable physical properties of the resultant moulded parts, such as mechanical strength and resistance to temperature. In addition, the moulded part must have a low weight and good aesthetic properties. Also, there is a need for the materials from which the part is made to be economically and ecologically sound and to demonstrate sustainability.